PROJECT SUMMARY Mexican migrants traveling through the U.S.-Mexico border region represent a large, highly mobile, and socially vulnerable subset of Mexican nationals. Population-level health data for this group is hard to obtain given their geographic dispersion, mobility, and largely undocumented status. Over the last 9 years, we have adopted a unique migration framework and novel methodological approach to characterize disease burden, health behaviors, and exposure to protective and risk factors among these migrants. We have implemented probability surveys of Mexican migrant flows in Tijuana, Mexico, producing population-level health estimates for migrants in the premigration, transit, destination, interception/deportation, and return phases. To date, we have examined two health areas: HIV risk and access to health care. Findings from our previous phase have propelled the establishment of free prevention clinics in five deportation stations along the Mexican border with funding from the Mexican Secretariat of Health. Over the next 5 years, we propose to continue and expand this work by (a) extending the survey east to two additional border cities in order to reach migrants traveling from, through, and to other regions; and (b) examining additional health areas to obtain a more complete picture of Mexican migrant health. We will conduct 3 probability surveys of migrant flows in Tijuana, Nogales, and Nuevo Laredo (N=1,200 ea.). In addition to data on health status and health care access, each survey will have a special focus: 1) HIV and Sexual/Reproductive Health; 2) Non-communicable Disease; and 3) Mental Health and Substance Use. Interview and biometric data will be obtained to produce population-level estimates of health care access and health status, investigate variations in access and outcomes across migration phases, and explore the impact of health care and immigration policies on migrants' health. Ninety survey respondents will be enrolled in a pilot longitudinal study to test the feasibility of adding a longitudinal dimension to our methods. This project will consolidate a binational observatory at the Mexico ? U.S. border and will generate critical data on migrant health. The data will become an important resource for migrant health scholars and will inform policy and programmatic responses to increase access to health care and improve the health status of migrants in sending, transit, and receiving communities.